The present invention relates to a liquid crystal module having a combination of a liquid crystal cell and a flexible relay board formed with a COF, and more particularly to a liquid crystal module in which individual and practical lead terminals of lead terminal rows of a flexible relay board such as a chip-on-film are electrically connected to individual lead-out electrodes of lead-out electrode rows of a liquid crystal cell via a thermal compression bonding process.
In the liquid crystal cell used in a display for displaying an image, on an edge part of one glass substrate of the glass substrates which are bonded to each other, many lead-out electrodes are arranged in parallel along the edge. As means for connecting a control circuit mounted on a wiring board to such a liquid crystal cell, the flexible relay board is used. For the flexible relay board, various kinds of boards called TCP, TAB and FPC rich in their flexibility are used as well as the chip-on-film (COF).
The flexible relay board formed with the above-described COF will be described below. In the flexible relay board, lead terminal rows having many practical lead terminals and dummy terminals arranged in parallel are formed on a base film made of a resin film such as polyimide resin. When the flexible relay board is electrically connected to the above-described liquid crystal, the individual and practical lead terminals of the lead terminal rows of the flexible relay board are positioned to and overlapped on the individual lead-out electrodes of the lead-out electrode rows of the liquid crystal cell to carry out a thermal compression bonding process in which the overlapped positions of them are pressurized and heated.
As shown in FIGS. 5 to 7, lead-out electrode rows 20 are formed on an edge part of a glass substrate 11 of one side of a liquid crystal cell 10. In the lead-out electrode rows 20 of an illustrated example, many lead-out electrodes 21 densely arranged in parallel at equal pitches P1 are included.
As compared therewith, in a flexible relay board 50 to be combined with the liquid crystal cell 10, lead terminal rows 60 are formed on an edge part of a rectangular base film 51 on which a liquid crystal control circuit (not shown in the drawing) including an IC chip is formed. In the lead terminal rows 60, many practical lead terminals 61 arranged in parallel and a prescribed number of dummy terminals 65 are included. In the lead terminal rows 60 of an illustrated example, at both sides in row ends of a practical lead terminal row 62 composed of many practical lead terminals 61 respectively, two dummy terminals 65 and 65 are adjacently arranged in parallel.
In FIG. 5, the illustrations of the lead-out electrodes 21 or the practical lead terminals 61 located in an intermediate part in the direction of an arrangement are omitted. Further, a hatching is applied to the dummy terminals 65 and 65.
To the above-described liquid crystal cell 10 and the flexible relay board 50, as marks useful for individually positioning the individual practical lead terminal 61 or the dummy terminals 65 included in the lead terminal rows 60 in the flexible relay board 50 side to the individual lead-out electrodes 21 included in the lead-out electrode rows 20 in the liquid crystal cell 10 side, alignment marks M1 and M2 are respectively attached. The alignment marks M1 and M2 are located at both sides sandwiching the above-described lead-out electrodes row 20 and at both sides sandwiching the lead terminal row 60.
As a method for positioning the individual lead-out electrodes 21 of the liquid crystal cell 10 side and the individual practical lead terminals 61 of the flexible relay board 50 side by using the alignment marks M1 and M2 as the marks, are exemplified a method by an automatic machine and a method of a visual recognition by using a manual machine. The method of the visual recognition by using the manual machine is a method that an operator decides the suitability of an overlapped state of the alignment marks M1 and M2 enlarged and displayed on a monitor by visually recognizing the overlapped state of the marks.
In the above-described thermal compression bonding process, since the overlapped positions of the individual lead-out electrodes 21 of the liquid crystal cell 10 side and the individual practical lead terminals 61 or the dummy terminals 65 of the flexible relay board 50 side are pressurized and heated, the base film 51 of the flexible relay board 50 is thermally expanded to be extended in the direction along the lead terminal rows 60. In accordance with the extension of the base film 51, the pitches between the practical lead terminals 61, the pitches between the dummy terminals 65 and the practical lead terminals 61 and the pitches between the dummy terminals 65 included in the lead terminal rows 60 are increased. The pitches between them are the same. The pitches between them are shown by a sign P2 in FIG. 6.
Thus, in the flexible relay board 50 used in the usual liquid crystal module, a treatment is carried out in which the extension is corrected only in the positions of the practical lead terminals 61 or the dummy terminals 65 of the lead terminal rows 60 by considering the extension percentage of the base film in the thermal compression bonding process, and on the other hand, the extension is not corrected in the positions of the alignment marks M2.
Therefore, in the flexible relay board 50 before the thermal compression bonding process is carried out, as can be understood from FIG. 6, the pitches between the practical lead terminals 61 or the pitches between the dummy terminals 65 and the practical lead terminals 61 (both the pitches are shown by P2) in the flexible relay board 50 side are narrower than pitches P1 between the lead-out electrodes 21 of the liquid crystal cell 10 side. Accordingly, when the alignment marks M1 and M2 of the liquid crystal cell 10 and the flexible relay board 50 respectively are mutually overlapped, the dummy terminal 65 at the row end of the flexible relay board 50 side is located more inside by an amount shown by a sign δ than the lead-out electrode 21 at the row end of the liquid crystal cell 10 side. Then, when the thermal compression bonding process is carried out, as shown in FIG. 7, the base film 51 of the flexible relay board 50 is extended by an amount meeting the extension percentage as shown by an arrow mark A. Thus, the individual practical lead terminals 61 or the individual dummy terminals 65 in the flexible relay board 50 side are separately thermally compression boded to and electrically connected to the individual lead-out electrodes 21 in the liquid crystal cell 10 side.
On the other hand, in the field of the liquid crystal module, a countermeasure is proposed in which an extension correction amount is set after a thermal compression bonding process is applied to a flexible board having a plurality of terminal blocks to connect electrode terminals of the flexible board to electrode terminals of a liquid cell side without a misalignment in all the terminal blocks (for instance, Patent Document 1).
Further, a countermeasure is also proposed in which either pitches of terminals of lead-out electrodes in a liquid cell side or pitches of terminals of output electrode terminal in a flexible board side are set to be constant, and for the other pitches of the terminals, a correction of an extension meeting a coefficient of thermal expansion of the flexible board is set to be small in the central part of the terminal part and to be larger as the terminal part comes nearer to an end side to reduce an imperfect connection (for instance, Patent Document 2).    [Patent Document 1] Japanese Patent Publication Number 2004-87608 A    [Patent Document 2] Japanese Patent Publication Number 2000-312070 A
As described above, in the liquid crystal module according to the usual example described by referring to FIGS. 5 to 7, when the positioning method by the visual recognition is carried out by using the manual machine, the operator decides the suitability of the overlapped state of the alignment marks M1 and M2 enlarged and displayed on the monitor by visually recognizing it.
However, as shown in FIG. 8, the size of the alignment mark M2 is exceptionally larger than the width of the pitches P2 between the practical lead terminals 61 or the dummy terminals 65. For instance, when the pitches P2 between the practical lead terminals 61 or the dummy terminals 65 is 0.05 mm in the flexible relay board 50, the size of the alignment mark M2 is about two times as large as 0.02 mm. Therefore, when the positioning method by the visual recognition is carried out by using the manual machine, even if the operator decides that the overlapped state of the alignment marks M1 and M2 enlarged and displayed on the monitor is suitable by visually recognizing it, the practical lead terminals 61 or the dummy terminals 65 in the flexible relay board 50 side are not necessarily precisely overlapped on the individual lead-out electrodes 21 in the liquid crystal cell 10 side.